Synthesis of α‐glucans in fission yeast spores is carried out by three α‐glucan synthase paralogues, Mok12p, Mok13p and Mok14p

Summary Fission yeast possesses a family of (1,3)‐α‐glucan synthase‐related genes; one of them, mok1 + / ags1 + , plays an essential function in morphogenesis during vegetative growth. Here we show that three mok1 + paralogues – mok12 + , mok13 + and mok14 + – are required for sporulation to succeed, acting at different stages of the spore wall maturation process. Mutation of mok12 + affected the efficiency of spore formation and spore viability. Deletion of mok13 + does not affect spore viability but the spores showed reduced resistance to stress conditions. mok14 Δ mutant spores failed to accumulate the amylose‐like spore wall‐specific polymer. mok12 + , mok13 + and mok14 + expression was restricted to sporulating cells and the proteins localized to the spore envelope but with different timing. mok11 + was also induced during the sporulation process although its deletion did not show apparently a sporulation defect. In vegetative cells, β‐glucans are more abundant than α‐glucans (55% versus 28%). In spores, the situation was the opposite, α‐glucans accounted for 46% while β‐glucans were approximately 38% of the total polysaccharides. We found at least two types of α‐glucan polymers, Mok12p and Mok13p, were involved in the synthesis of the greater part of α‐glucan in the spores envelope, a polymer that is mainly digested with α‐1,3 glucanase, while Mok14p, homologous to starch synthases, was required for the synthesis of the iodine‐reactive polymer that is made of α‐1,4 glucose residues.